1. Field of the Invention
The present invention relates to a voltage multiplying circuit, and particularly relates to a voltage multiplying circuit that can save the number of capacitors.
2. Description of the Prior Art
In many electronic apparatuses, a voltage multiplying circuit is always utilized to generate a desired voltage. Please note that the voltage multiplying circuit is not limited to a double voltage multiplying circuit. It can also mean a triplicity voltage multiplying circuit, a quadruple voltage multiplying circuit or a voltage multiplying circuit with a higher multiple. A charge pump type voltage increasing circuit is a popular voltage multiplying circuit. FIG. 1 illustrates a prior art voltage multiplying circuit. As shown in FIG. 1, the voltage multiplying circuit includes four transistors 101, 103, 105 and 107, which are selectively coupled a voltage VCI, a voltage VCDD, a voltage AVEE and a ground voltage level GND via the switch elements 107-121. Conventionally, the voltage AVDD equals twice of the voltage VCI, and the voltage AVEE equals minus twice of the voltage VCI.
The capacitors 103 and 107 are utilized for voltage stabling capacitors, thus the voltages thereon are fixed. However, the voltages of the capacitors 101 and 105 float instead of fixed. The voltage multiplying circuit disclosed in FIG. 1 includes two phases (the first phase Φ1 and the second phase Φ2, or called the first mode and the second mode). In the first phase Φ1, the switch elements 108, 109 are conductive, thus the voltage VCI charges the capacitor 101. Besides, the switch elements 115, 117 are also conductive, thus the voltage AVDD charges the capacitor 105. In this case, the voltage on the capacitor approaches twice VCI and the voltage on the capacitor 101 approaches VCI. In the second phase Φ2, the switch elements 111, 113 are conductive. In this case, the capacitor 101 can be regarded as a battery, thus the capacitor 101 is series-connected with the voltage VCI to generate a voltage 2VCI. Additionally, the switch devices 119, 121 are also conductive. In this case, the capacitor 105 can be regarded as a battery, thus the capacitor 105 is parallel-connected with the voltage AVEE to generate a voltage −2*VCI.
Via thus structure, a desired voltage can be acquired. However, since a voltage stabling capacitor is utilized, this kind of circuit needs more capacitors, such that manufacturing cost and design complexity increases.